From a careful examination of the Vedas and Upanishads it is found that the ancient Hindus did not believe in the doctrine of transmigration, but held, as so many theosophists do, that “once a man, always a man,” but of course there is the exception of the case where men live bad lives persistently for ages. But it also seems very clear that the later Brahmins, for the purpose of having a priestly hold on the people or for other purposes, taught them the doctrine that they and their parents might go after death into the bodies of animals. Though it may not be acceptable for many, some hold it as a belief because they saw the Hindu and the Jain alike acting very carefully as to animals and insects, avoiding them in the path, carefully brushing insects out of the way at a great loss of time, so as to not step on them.
First, the permanence of the essential self: the essential self, the Supreme Being is believed to exist in all serenity and aloofness, for without the assumption of a permanent entity, the talk of rebirths meaningless.
Second, the operation of the original ignorance: the whole process of rebirth is made possible by the operation of the original ignorance, avidya, in causing the essential self to assume individuality. There it is conditioned by the mind-body complex, and is involved in the world of human existence.
Third, the possibility of union with the Supreme Being: the self is under ignorance and is united to the body. There are two possibilities: either the individual through true knowledge returns to the original state of the essential self, that is, attains liberation- moksa, or the individual continues his pilgrimage through various rebirths until he finally reaches the goal of liberation.
Fourth, the doctrine of karma: the doctrine of karma is the solution offered by Hinduism to the great riddle of the origin of suffering and inequalities which exist among men in the world.